Mutual interference between wireless devices is a well-known problem. At a basic level, when two devices attempt to exchange information, the devices typically coordinate their transmit times so that they are not transmitting to each other simultaneously. When more devices are added to form a network, each additional device must also coordinate its transmit time so that two or more devices do not simultaneously transmit to a network hub. Networks may designate specific transmit times for each device. However, this solution becomes more complicated as new devices are added to a network and the available transmit times are used up.
The interference-avoidance problem becomes more complicated when multiple networks operate in the same area. Two or more neighboring networks may experience transmission collisions not only between nodes in the same network, but also between nodes in the separate networks. Frequency separation may be used to avoid transmission collisions between these separate networks. However, this solution will not work when the multiple devices must transmit on a common channel, such as when two networks happen to operate on the same channel for intended or unintended reasons.
For ad hoc networks that can be formed in any location, spatial separation cannot be used to avoid transmission collisions on the same channel. Accordingly, there is a need for a procedure to avoid mutual interference among networks that transmit on the same or adjacent frequency bands.